US 8,374,573 B1Granted

AVI system with improved receiver signal processing

AssigneeReno A & E

InventorThomas R. Potter, Sr.

Life of this patent

Estimating the term…

Loading patent…

Abstract

An automatic vehicle identification (AVI) system signal processing technique which provides improved performance and reliability and which substantially eliminates the adverse effect of ambient noise signals on the detection of permissible code sequences by an AVI receiver. Input signals to an AVI receiver are filtered to strip off all frequency components except those at the carrier frequency. The filtered signals are subjected to variable gain amplification over a substantially linear operating range with the maximum amplitude of the amplified signals limited to a maximum value below the supply voltage and within the linear range of the variable gain amplifier. The amplified signals are converted to a binary pulse train signifying the temporal length of each active carrier period and the temporal length of each quiescent carrier period. The binary pulse train is decoded and a valid vehicle signal is generated if the decoded binary pulse train matches a permissible code sequence.

Claims22

Dependent claims

An automatic vehicle identification (AVI) receiver for processing signals received thereby to recover information encoded in carrier frequency signals generated at a specific frequency by a transmitter and identifying an authorized vehicle, said receiver comprising:

an input terminal adapted to be coupled to an inductive loop defining a detection zone for receiving signals from the loop;
a filter unit coupled to said input terminal for permitting signals at said specific frequency present on said input terminal to pass therethrough and for substantially attenuating all other frequency components of signals present on said input terminal, said filter unit having an output;
a variable gain amplifier having an input coupled to said output of said filter unit for amplifying signals input thereto and for limiting the amplitude of signals amplified thereby to a maximum value, said variable gain amplifier having a gain control signal input and an output, said variable gain amplifier having an operating range with a linear portion;
an amplitude detection circuit having an input coupled to said output of said variable gain amplifier and a gain control signal output coupled to said gain control input of said variable gain amplifier for sensing the amplitude of signals received from said variable gain amplifier and for generating a gain control signal for controlling the gain of said variable gain amplifier so that the signals input to said variable gain amplifier are operated on within said linear portion and the amplitude of signals amplified by said variable gain amplifier are limited to said maximum value;
and
a carrier-to-pulse conditioning circuit having an input coupled to said output of said variable gain amplifier for converting carrier frequency signals present at the output of said variable gain amplifier to a binary pulse train signifying the temporal length of each active carrier period and the temporal length of each quiescent carrier period, said carrier-to-pulse conditioning circuit having an output.

3 more elements

A method of processing signals received by an automatic vehicle identification (AVI) receiver to recover information encoded in carrier frequency signals generated at a specific frequency by a transmitter and identifying an authorized vehicle, said method comprising the steps of:

(a) filtering signals received by the receiver to permit signals at said specific frequency to pass for further processing and for substantially attenuating all other frequency components of received signals;
(b) providing a reference supply voltage;
(c) processing the signals filtered in step (a) with a variable gain amplifier having an operating range with a linear portion to produce amplified carrier frequency signals operated on within the linear portion and having a maximum amplitude limited to a maximum value lower than the reference supply voltage;
and
(d) converting the amplified signals from step (c) to a binary pulse train signifying the temporal length of each active carrier period and the temporal length of each quiescent carrier period, said step (d) of converting including the steps of:
(i) establishing a first trigger threshold for carrier frequency signals amplified in step (c), and;
(ii) generating a binary signal at a first level when the amplified signal rises above the first trigger threshold at the beginning of an active carrier period and generating a binary signal at a second level when the amplified signal falls below the first trigger threshold at the end of an active carrier period.

4 more elements

Dependencies are inferred from the claim text.